Ceramics 3 Flashcards
what are the indications for zirconia-based ceramics?
- ant and post crowns
- 3-4 unit bridges for ant and post
- implant abutments
- inlay bridges
- maryland bridges
- blocking out darkened tooth structure or cores
what are the contraindications and limitations of zirconia based ceramics?
- for long-span bridges (must follow manufactuer’s guidelines)
- cantilever bridges, inlays/onlays, veneers
- if using for partial dentures–need precision or semi-precision attachments
advantages of zirconia based ceramics?
- metal free
- translucent compared to other ceramic-metal restos
- can be used for posterior bridges
- cementation with traditional cements
- high flexural strength and fracture toughness
- can be used with zirconia-based implant materials
- block out of discoloured core material
- more cost-effective when high noble metal prices are high
what are disadvantages of zirconia-based ceramics?
- limits on bridge spans
- generally require more axial reduction
- due to OUTSOURCING, lab fabrication times may be longer
why is pure zirconia ceramic impossible to fabricate?
during cooling, it goes from tetragonal to monoclinic cause expansion and induces very large stressed–>ZrO2 will crac at room temp; so we can use dpants (CaO, MgO2, Y2O3, CeO2) to stabilize the tetragonal or cubic form at room temp (e.g. the more Y2O3 you add, the more cubic form you retain
describe how expansion can prevent crack propagation in zirconia ceramics
when a crack hits the tetragonal phase, the tetragonal phase will trnsform to monoclinic, which cause a 3-4% expansion–>puts crack into compression and closes it; enhances Kic (toughness)
what are the types of pressing and which are strongest?
- axial–weakest
- CIP 2D –> medium strongest
- CIP 3D –> strongest
pressing is the main reason why stuff is more expressive and stronger
pores less than 5 um are not critical and will not adversely effect zirconia ceramics; but elongated cracks and sharp defects will
ye
what is the sequence of events in machining?
powder is created–>pressed->debonded–>presintered–>machined–>sintered
what is hot isostatic pressing?
- includes application of high pressure and temp via a gas such as argon and nitrogen to DENSIFY and INCREASE physical properties
HOW DOES GRAIN SIZE AND ZIRCONIA STRCUTURE RELATE
the smaller the grain, the lowe rhe transformation of tetragonal to monoclinic when qcooling
why shouldn’t we grind a xirconia ceramic resto after it has been processed in the lab?
can creat small grooves–>cracks–>stress concentration, fracture, higher failure rates
decreases the RELIABILITY of zirconia
also these grooves cause critical defects which DECREASE the FATIGUE limit of zirconia ceramics
growth of transformation of one grain (t–>m) causes stress on neighbouring grains = growth of transformed zone = extensive microcracking and surface rougening
ye
a general rule: as FLEXURAL STRENGTH increase, ESTHETICS decreases; therefore, we can mix strong zirconia and esthetic feldspathic glass for the best of both worlds
ye
what is a major adv of veneers?
requires minimal reduction of tooth structure
